1. Field of Invention
The present invention relates to a method for assaying nucleic acids which can efficiently detect nucleic acids, etc. by fluorescence.
2. Related Art
In medical and biological fields, a means for labeling, for example, a DNA (or RNA) probe with a radioactive isotope, hybridizing the labeled probe with a target nucleic acid and then detecting the target nucleic acid by autoradiography has been currently performed widely.
However, the isotope method involves many drawbacks which are serious obstacles to application and development of this technology.
The drawbacks of the isotope method are as follows.
(a) In nucleic acid hybridization, the isotope method lacks any spatial resolution sufficient to reveal relative positional relationship between contiguous signal. PA1 (b) Experimental procedures using isotopes can only be carried out in isotope laboratories equipped with special facilities. This is a cause for hindering application of the hybridization method especially to clinical inspection. PA1 (c) Use of isotope is dangerous for laboratory workers even in laboratories. In addition, a danger for ordinary people also always exists because of wastes, etc. PA1 (d) A long time (several weeks to several months) may be required for detection, so application to rapid clinical diagnostics is difficult. PA1 (e) Radioactivity decays with a definite half-life period so that experiments should be scheduled to fit a purchase date of the isotope. If the schedule chart is slightly altered, there would be a danger of wasting isotope or experimental results in a large scale. PA1 (f) In order to enhance detect ion sensitivity, it is required to incorporate radioactivity to the nucleic acid probe as high as possible. However, the nucleic acid labeled enough to increase its radioactivity easily suffers from radioactive disintegration. PA1 (g) In general, isotope is extremely expensive and it is not unusual to use isotope worth several hundred yen in one run. This prevents general spread of the hybridization method.
In view of such background, some DNA or RNA labeling methods in place of radioactive isotope have been developed so far. For example, BLU GENE KIT commercially available from Bethesda Research Laboratories Inc. (BRL Inc.) is known. Furthermore, "Nucleic acid probe and use thereof" is disclosed in Japanese Patent Application Laid-Open No. 60-226888.
However, these techniques merely eliminate a part of the drawbacks described above. In particular, detection sensitivity is not comparable to that of the isotope method.
In view of such problems, an object of the present invention is to provide a method for assaying nucleic acids which solves the drawbacks of safety precautions, etc. in the isotope method and provides excellent detection sensitivity.